1. Field of the Invention
The present invention relates to novel silica particulates especially well adapted for incorporation into dentifrice compositions, to a process for the production of such novel particulates, and to improved dentifrice compositions comprising same.
2. Description of the Prior Art
It is known to this art that silica is a useful material for incorporation into dentifrice compositions. It performs a variety of different functions therein.
Firstly, it serves as an abrasive agent, thus mechanically contributing to the elimination of dental plaque.
It may also serve as a thickening agent to impart particular rheological properties to the dentifrice, as well as a colorant to impart particular coloration to the composition.
It is also known to this art that dentifrices contain various active agents, in particular for the prevention of dental caries, to reduce the formation of dental plaque or the deposition of tartar on the teeth. Among such agents, the fluorides and the zinc compounds are especially representative. Other elements are also incorporated, such as phosphates, pyrophosphates, polyphosphates, polyphosphonates, guanidines, in particular the bisbiguanides, and one of the compounds most typically included is chlorhexidine. Dentifrice formulations may also contain flavorants, perfumes, and the like.
The dentifrice compositions can also contain organic amino compounds. By the term "organic amino compounds" is intended any active molecule present in the dentifrice formulation and containing at least one nitrogen atom. Particularly representative of such organic amino compounds are (1) the fluorine-containing amines useful for caries prophylaxis and especially long-chain amino acid or amino addition products with hydrogen fluoride, such as cetyl amine hydrofluoride, bis(hydroxyethyl)-aminopropyl-N-hydroxyethyl octadecyl amine dihydrofluoride, octadecyl amine fluoride and N,N',N'-tri-(polyoxyethylene)-N-hexadecyl propylene diamene dihydrofluoride; (2) amino oxides useful as nonionic surfactants prepared by oxidation of tertiary aliphatic amines with hydrogen peroxide, especially the alkyl amine oxides of the formula R(CH.sub.3).sub.2 N.fwdarw.O, in which R is a straight or branched chain alkyl radical having approximately 10 to 24 carbon atoms, and the amine oxides of the formula R(CH.sub.2 CH.sub.2 OH).sub.2 N.fwdarw.O, in which R is as defined above; (3) alkyl amines, which can be primary, secondary, tertiary or quaternary aliphatic amines useful as cationic surfactants, such as those of the formula R--CH.sub.2 NH.sub.2, or dimethyl alkyl amines of the formula R-- N(CH.sub.3).sub.2 and cetyl trimethyl ammonium bromide; and (4) alkyl betaines, which are N-alkyl derivatives of N-dimethyl glycine and alkyl amidoalkyl betaines, designated hereinafter as "alkyl betaines".
Exemplary of this class of amphoteric surfactants are the alkyl betaines of the formula: ##STR1## and the alkyl amidopropyl dimethyl betaines of the formula: ##STR2## wherein R is a straight or branched chain alkyl radical having 10 to 24 carbon atoms.
A certain number of metal cations can be present in dentifrice compositions. Exemplary thereof are the alkaline earth metal cations, particularly calcium, strontium, barium, cations of Group IIIa, aluminum, indium, cations of Group IVa, germanium, tin, lead and cations of Group VIII, manganese, iron, nickel, zinc, titanium, zirconium, palladium, and the like. Such cations can be in the form of inorganic salts, e.g., the chloride, fluoride, nitrate, phosphate or sulfate, or in the form of organic salts, such as the acetate, citrate, and the like.
More specific examples of such salts are zinc citrate, zinc sulfate, strontium chloride, tin fluoride in the form of the single salt (SnF.sub.2) or the double salt (SnF.sub.2 /KF), stannous chlorofluoride SnClF and zinc fluoride (ZnF.sub.2).
The presence of the above-mentioned agents in the dentifrice presents the problem of their compatibility with silica. In effect, due particularly to its absorbent properties, the latter may have a tendency to react with these agents such that they are no longer available to elicit their aforesaid therapeutic and/or useful responses.
French Patent Application 87/15,276 describes silica particulates compatible with zinc. However, the silicas described do not exhibit a completely adequate compatibility with other metal cations, such as tin, strontium, and the like.